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Abstract:

A polyethylene resin having a multimodal molecular weight distribution
comprising at least two polyethylene fractions A and B, fraction A being
substantially free of comonomer and having a lower weight average
molecular weight and a higher density than fraction B, each fraction
prepared in different reactors of two reactors connected in series in the
presence of a Ziegler-Natta catalyst system, the polyethylene resin
having a density of from 0.950 to 0.965 g/cm3 and a melt index MI2
of from 0.5 to 5 g/10 min.

Claims:

1. A polyethylene resin having a multimodal molecular weight distribution
comprising at least two polyethylene fractions A and B, fraction A being
substantially free of comonomer and having a lower weight average
molecular weight and a higher density than fraction B, each fraction
prepared in different reactors of two reactors connected in series in the
presence of a Ziegler-Natta catalyst system, the polyethylene resin
having a density of from 0.950 to 0.965 g/cm3, measured following
the method of standard test ASTM 1505 at a temperature of 23.degree. C.,
a melt index MI2 of from 0.5 to 5 g/10 min, measured following the method
of standard test ASTM D 1238 at a temperature of 190.degree. C. and under
a load of 2.16 kg, and molecular weight distribution Mw/Mn of from 5 to
20.

2. The polyethylene resin of claim 1 wherein the Ziegler-Natta catalyst
system comprises a Ziegler-Natta catalyst component D and a preactivating
agent, wherein the Ziegler Natta catalyst component D is obtainable by a)
generating a reaction product A by contacting a magnesium dialkoxide
compound with a halogenating agent; b) contacting reaction product A with
a first halogenating/titanating agent to form reaction product B; c)
contacting reaction product B with a second halogenating/titanating agent
to form reaction product C; and d) contacting reaction product C with a
third halogenating/titanating agent to form catalyst component D.

3. The polyethylene resin according to claim 2 wherein the preactivating
agent of the catalyst system is an organoaluminium compound, preferably
triethyl aluminium (TEAL).

4. The polyethylene resin according to claim 1 wherein at least one of
the reactors is a slurry loop reactor.

5. The polyethylene resin according to claim 4 wherein the two reactors
are slurry loop reactors.

6. The polyethylene resin according to claim 1 wherein fraction B is
produced in the first reactor and fraction A is produced in the second
reactor.

7. The polyethylene resin according to claim 1 having an environmental
stress crack resistance measured with 100% Igepal CO-630 of at least 100
h, preferably at least 400 h.

8. An injection stretch blow moulded container prepared with a
polyethylene resin according to claim 1.

9. The injection stretch blow moulded container according to claim 8
wherein the container weighs from 10 to 150 g per dm3 of volume.

10. The injection stretch blow moulded container according to claim 9
wherein: the container weighs from 10 to 150 g per dm3 of volume,
when the container has a volume of less than 300 cm3, the container
weighs from 10 to 80 g per dm3 of volume, when the container has a
volume of at least 300 cm.sup.3.

11. Use of the resin according to claim 1 for injection stretch blow
moulding applications.

12. Use of a stretch blow moulded container according to claim 8 in food
applications in particular the packaging of juices, dry products and
dairy products and in non-food applications in particular the packaging
of cosmetic, detergents and pharmaceutical products.

Description:

FIELD OF THE INVENTION

[0001] The present invention relates to a polyethylene resin with a
multimodal, preferably bimodal, molecular weight distribution for the
preparation of polyethylene preforms for one- or two-stage
injection-stretch-blow-moulding (ISBM) processes and to the ISBM articles
produced therefrom.

BACKGROUND OF THE INVENTION

[0002] Injection-stretch blow molding (ISBM) is a process widely used for
the production of containers, such as bottles, using thermoplastic
polymers. The process includes the steps of preparing a pre-form by
injection molding and then expanding the pre-form to the desired final
shape. In general, one distinguishes one-stage and two-stage processes.
In the one-stage process the steps of producing the pre-form and
expanding the pre-form to the desired final shape are performed in the
same machine. In the two-stage process these two steps are performed in
different machines, in some cases even in different geographical
locations; the pre-form is allowed to cool to ambient temperature and is
then transported to a second machine where it is reheated and expanded to
the desired final shape. Due to reasons of production speed and
flexibility the two-stage process is preferred for larger production
volumes.

[0003] Recent progress in development has made polypropylene a viable
alternative to polyethylene terephthalate (PET) for injection-stretch
blow molding (ISBM). Due to their good optical properties
propylene-ethylene random copolymers are the preferred polypropylene
grades.

[0004] For the injection molding of polypropylene it is well known to
improve the impact performance, while also having good optical
properties, by the addition of a polyethylene, which has been produced
using a metallocene catalyst.

[0005] For example, EP-A-151741 to Mitsui discloses single-stage
manufacturing of articles by ISBM. These articles are prepared from
propylene-ethylene random copolymers having a melt flow index of from 4
to 50 dg/min and containing a nucleating agent.

[0006] WO95111791 to Bekum is directed to a two-stage process for
preparing articles by ISBM. The preferred resin is an ethylene-propylene
copolymer containing more than 50 wt % of propylene and having a melt
index of from 10 to 20 dg/min.

[0007] WO 2005/005143 to Total Petrochemicals discloses blow-molded
containers made from a blend of polypropylene and a metallocene
polyethylene to improve the impact strength.

[0008] The polypropylenes presently used in injection-stretch blow molding
applications allow for the production of containers with good optical
properties at industrially viable production rates. However, as compared
to other polymers used in injection-stretch blow molding polypropylene
suffers from a lack of the combination of high rigidity and high ESCR, as
well as high impact strength, particularly at lower temperatures.

[0009] Thus, there is an interest for improving the impact performance,
rigidity and ESCR of injection-stretch blow molded containers. A balance
has to be found between the high fluidity required for the first step to
form the preform and the lower fluidity required for the second step when
blowing the preform.

[0010] JP2000086722 to Asahi discloses the use of high-density
polyethylene, preferaby prepared with a metallocene catalyst, suitable
for injection stretch blow molding.

[0011] JP2000086833 to Asahi discloses the use of resin compositions
suitable for injection stretch blow molding at a high stretch ratio,
comprising a polyethylene prepared with a metallocene catalyst and and a
polyethylene prepared with a chromium catalyst.

[0012] JP9194534 to Mitsui discloses the use of a polyethylene-based resin
for injection stretch blow molding having a density of 0.940 to 0.968
g/cm3 and a melt flow index of 0.3 to 10 g/10 min (ASTM D1238 at
190° C. and 2.16 kg).

[0013] It is an aim of the invention to provide a polyethylene resin for
injection stretch blow moulding with a broad processing window.

[0014] It is also an aim of the invention to provide a polyethylene resin
for injection stretch blow moulding with good process stability.

[0015] It is an aim of the invention to provide a polyethylene resin for
injection stretch blow moulding with a high environmental stress crack
resistance (ESCR measured with 100% Igepal CO-630). The environmental
stress crack resistance is advantageously of at least 100 h, preferably
at least 400 h.

[0016] In addition is an aim of the invention to provide a polyethylene
resin for injection stretch blow moulding with a high impact resistance.

[0017] Furthermore, it is an aim of the invention to provide a
polyethylene resin for injection stretch blow moulding with high
rigidity.

[0018] In addition, it is also an aim of the invention to provide a
polyethylene resin for injection stretch blow moulding to prepare
containers with a high top load. The top load is the ability of a
standing bottle to withstand the weight of other bottles on pallets.

[0019] It is further an aim of the invention to provide a polyethylene
resin for injection stretch blow moulding to prepare containers with good
thickness repartition.

[0020] It is additionally an aim of the invention to provide a
polyethylene resin for injection stretch blow moulding to prepare
containers with good surface aspects.

[0021] It is furthermore an aim of the invention to provide a polyethylene
resin for injection stretch blow moulding to prepare containers with good
finishing for molded drawings.

[0022] Finally, it is also an aim of the invention to provide a
polyethylene resin suitable for injection stretch blow moulded containers
for consumer packaging, in particular for cosmetics and detergents.

[0023] At least one of these aims is fulfilled by the resin of the present
invention.

BRIEF DESCRIPTION OF THE DRAWING

[0024] FIG. 1 shows the molecular weight distribution of two polyethylene
resins having a bimodal molecular weight distribution, Grade Y being a
resin according to the invention. The bimodality is shown as a shoulder
on the gaussian curve at around Log(M)=4.8

[0025]FIG. 2 shows a bottle obtained by ISBM with Grade Z according to
the examples

[0026] FIG. 3 shows a preform with random flow lines (made with Grade X
according to the examples)

[0027] FIG. 4 shows the side view of an ISBM bottle made with Grade X
according to a comparative example

[0028] FIG. 5 shows the bottom view of a an ISBM bottle made with Grade Y
according to the invention

[0029] FIG. 6 shows the schematics of a bottle design

[0030] FIG. 7 shows an ISBM Bottle made with Grade Y according to the
invention

SUMMARY OF THE INVENTION

[0031] A polyethylene resin having a multimodal molecular weight
distribution comprising at least two polyethylene fractions A and B,
fraction A being substantially free of comonomer and having a lower
weight average molecular weight than fraction B and a higher density than
fraction B, each fraction prepared in different reactors of two reactors
connected in series in the presence of a Ziegler-Natta catalyst system,
the polyethylene resin having a density of from 0.950 to 0.965
g/cm3, measured following the method of standard test ASTM 1505 at a
temperature of 23° C., a melt index MI2 of from 0.5 to 5 g/10 min,
measured following the method of standard test ASTM D 1238 at a
temperature of 190° C. and under a load of 2.16 kg, and molecular
weight distribution Mw/Mn of from 5 to 20.

[0032] By "substantially free of comonomer" it is meant that the
polymerisation step to obtain the polyethylene fraction A is carried out
in the absence of comonomer.

[0033] The resin according to the invention is particularly suitable for
injection stretch blow moulding (ISBM). Thus the invention also covers
injection stretch blow moulded articles, in particular containers,
preferably containers for consumer packaging e.g. for cosmetics or
detergents, as well as the use of the resin according to the invention
for ISBM applications.

[0034] The process for obtaining the resin is also included herein.

DETAILED DESCRIPTION OF THE INVENTION

[0035] The Polyethylene Resin

[0036] The polyethylene resin having a multimodal, preferably bimodal,
molecular weight distribution according to the present invention can be
produced by polymerizing ethylene and one or more optional comonomers in
the presence of a Ziegler-Natta catalyst system in two or more reactors
connected in series. Due to the use of two or more reactors, the resin
according to the invention comprises a high molecular weight (HMW), low
density fraction and a low molecular weight (LMW), high density fraction.

[0037] Any Ziegler-Natta system known to the person skilled in the art can
be used. A preferred Ziegler-Natta catalyst system comprises a titanium
compound having at least one titanium-halogen bond and an internal
electron donor, both on a suitable support (for example on a magnesium
halide in active form), an organoaluminium compound (such as an aluminium
trialkyl), and an optional external donor.

[0038] More preferably, the Ziegler-Natta catalyst system used to prepare
the polyethylene resin of the present invention comprises a Ziegler-Natta
catalyst component D and a preactivating agent, wherein the Ziegler Natta
catalyst component D is obtainable by: [0039] a) generating a reaction
product A by contacting a magnesium dialkoxide compound with a
halogenating agent; [0040] b) contacting reaction product A with a first
halogenating/titanating agent to form reaction product B; [0041] c)
contacting reaction product B with a second halogenating/titanating agent
to form reaction product C; and [0042] d) contacting reaction product C
with a third halogenating/titanating agent to form catalyst component D.

[0043] Products A and B are not be confused with the polyethylene
fractions A and B of the resin.

[0044] Preferably, the preactivating agent is an organoaluminium compound,
preferably of the formula AIR3, wherein R is an alkyl having 1-8
carbon atoms or a halide, and wherein each R may be the same or
different. More preferably, the organoaluminium compound is TEAL.

[0045] Preferably, the halogenating agent is ClTi(OPr)3.

[0046] Preferably, the first halogenating/titanating agent a mixture of
TiCl4 and Ti(OBu)4, in a molar ratio range of from 0.5:1 to 6:1
of TiCl4/Ti(OBu)4. More preferably the molar ratio is 2:1 of
TiCl4/Ti(OBu)4.

[0047] Preferably, the second halogenating/titanating agent is TiCl4.

[0048] Preferably, the third halogenating/titanating agent is also
TiCl4.

[0049] By "Ziegler-Natta catalyst system," we mean a Ziegler-Natta
catalyst component in combination with a preactivating agent.

[0050] By "Ziegler-Matta catalyst component," we mean a transition metal
compound that incorporates a Group 4-8 transition metal, preferably a
Group 4-6 transition metal, and one or more ligands that satisfy the
valence of the metal. The ligands are preferably halide, alkoxy, hydroxy,
oxo, alkyl, and combinations thereof. Ziegler-Matta catalysts exclude
metallocenes or other single-site catalysts.

[0051] It is thought that the Ziegler-Matta catalyst used in the process
of this invention without being bound to theory has the effect that the
resin has an overall higher molecular weight (i.e. higher extrudate
swell) without affecting the low molecular weight tailing (i.e. better
impact properties).

[0052] The present invention provides a polymerisation process wherein the
catalyst is preferably made according to a process comprising the
following steps:

[0053] a) contacting a magnesium dialkoxide compound with a halogenating
agent to form a reaction product A;

[0054] b) contacting reaction product A with a first
halogenating/titanating agent to form reaction product B;

[0055] c) contacting reaction product B with a second
halogenating/titanating agent to form reaction product C;

[0056] and d) contacting reaction product C with a third
halogenating/titanating agent to form reaction product D.

[0057] The second and third halogenating/titanating agents can comprise
titanium tetrachloride. The second and third halogenating/titanating
steps can each comprise a titanium to magnesium ratio in the range of
about 0.1 to 5. The reaction products A, B and C can each be washed with
a hydrocarbon solvent prior to subsequent halogenating/titanating steps.
The reaction product D can be washed with a hydrocarbon solvent until
titanium species [Ti] content is less than about 100 mmol/L.

[0058] Another embodiment of the present invention provides a polyolefin
catalyst produced by a process generally comprising contacting a catalyst
component of the invention together with an organometallic agent. The
catalyst component is produced by a process as described above. The
catalysts of the invention can have a fluff morphology amenable to
polymerization production processes, and may provide a polyethylene
having a molecular weight distribution of at least 5.0 and may provide
uniform particle size distributions with low levels of particles of less
than about 125 microns. The activity of the catalyst is dependent upon
the polymerization conditions. Generally the catalyst will have an
activity of at least 5,000 gPE/g catalyst, but the activity can also be
greater than 50,000 gPE/g catalyst or greater than 100,000 gPE/g
catalyst.

[0059] Even another embodiment of the present invention provides a
polyolefin polymer produced by a process comprising: a) contacting one or
more olefin monomers together in the presence of a catalyst of the
invention, under polymerization conditions; and b) extracting polyolefin
polymer. Generally the monomers are ethylene monomers and the polymer is
polyethylene.

[0060] According to one embodiment of the invention, a method for making a
catalyst component generally includes the steps of forming a metal
dialkoxide from a metal dialkyl and an alcohol, halogenating the metal
dialkoxide to form a reaction product, contacting the reaction product
with one or more halogenating/titanating agent in three or more steps to
form a catalyst component, and then treating the catalyst component with
a preactivation agent such as an organoaluminum.

[0061] One embodiment of the present invention can be generally as
follows:

[0062] 1. MRR'+2R''OH→M(OR'')2

[0063] 2. M(OR'')2+ClAR'''x→"A"

[0064] 3. "A"+TiCl4/Ti (OR''')4→"B"

[0065] 4. "B"+TiCl4→"C";

[0066] 5. "C"+TiCl4→"D"

[0067] 6. "D"+preactivating agent→catalyst

[0068] In the above formulas, M can be any suitable metal, usually a Group
IIA metal, typically Mg. In the above formulas, R, R', R', R''', and
R'''' are each independently hydrocarbyl or substituted hydrocarbyl
moieties, with R and R' having from 1 to 20 carbon atoms, generally from
1 to 10 carbon atoms, typically from 2 to 6 carbon atoms, and can have
from 2 to 4 carbon atoms. R'' generally comprises from 3 to 20 carbon
atoms, R''' generally comprises from 2-6 carbon atoms, and R''' generally
comprises from 2-6 carbon atoms and is typically butyl. Any combination
of two or more of R, R', R'', and R'''' can be used, may be the same, or
the combination of the R groups may be different from one another.

[0069] In the above embodiment comprising formula ClAR'''x, A is a
non-reducing oxyphilic compound which is capable of exchanging one
chloride for an alkoxide, R''' is a hydrocarbyl or substituted
hydrocarbyl, and x is the valence of A minus 1. Examples of A include
titanium, silicon, aluminum, carbon, tin and germanium, typically is
titanium or silicon wherein x is 3. Examples of R''' include methyl,
ethyl, propyl, isopropyl and the like having 2-6 carbon atoms.
Nonlimiting examples of a chlorinating agent that can be used in the
present invention are ClTi(OiPr)3 and ClSi(Me)3.

[0070] The metal dialkoxide of the above embodiment is chlorinated to form
a reaction product "A". While the exact composition of product "A" is
unknown, it is believed that it contains a partially chlorinated metal
compound, one example of which may be ClMg(OR'').

[0071] Reaction product "A" is then contacted with one or more
halogenating/titanating agent, such as for example a combination of
TiCl4 and Ti(OBu)4, to form reaction product "B". Reaction
product "B" which is probably a complex of chlorinated and partially
chlorinated metal and titanium compounds. Reaction product "B" can
comprise a titanium impregnated MgCl2 support and for example, may
possibly be represented by a compound such as (MCl2)y
(TiClx(OR)4-x)z. Reaction product "B" can be precipitated
as a solid from the catalyst slurry.

[0072] The second halogenation/titanation step produces reaction product,
or catalyst component, "C" which is also probably a complex of
halogenated and partially halogenated metal and titanium compounds but
different from "B" and may possibly be represented by (MCl2)y
(TiClx'(OR)4-x')z'. It is expected that the level of
halogenation of "C" would be greater than that of product "B". This
greater level of halogenation can produce a different complex of
compounds.

[0073] The third halogenation/titanation step produces a reaction product,
or catalyst component, "D" which is also probably a complex of
halogenated and partially halogenated metal and titanium compounds but
different from "B" and "C", and may possibly be represented by
(MCl2)y(TiClx''(OR)4-x'')z''. It is expected
that the level of halogenation of "D" would be greater than that of
product "C". This greater level of halogenation would produce a different
complex of compounds. While this description of the reaction products
offers the most probable explanation of the chemistry at this time, the
invention as described in the claims is not limited by this theoretical
mechanism.

[0074] Metal dialkyls and the resultant metal dialkoxides suitable for use
in the present invention can include any that can be utilized in the
present invention to yield a suitable polyolefin catalyst. These metal
dialkoxides and dialkyls can include Group IIA metal dialkoxides and
dialkyls. The metal dialkoxide or dialkyl can be a magnesium dialkoxide
or dialkyl. Non-limiting examples of suitable magnesium dialkyls include
diethyl magnesium, dipropyl magnesium, dibutyl magnesium,
butylethylmagnesium, etc. Butylethylmagnesium (BEM) is one suitable
magnesium dialkyl.

[0075] In the practice of the present invention, the metal dialkoxide can
be a magnesium compound of the general formula Mg(OR'')2 where R''
is a hydrocarbyl or substituted hydrocarbyl of 1 to 20 carbon atoms.

[0076] The metal dialkoxide can be soluble and is typically non-reducing.
A non-reducing compound has the advantage of forming MgCl2 instead
of insoluble species that can be formed by the reduction of compounds
such as MgRR', which can result in the formation of catalysts having a
broad particle size distribution. In addition, Mg(OR'')2, which is
less reactive than MgRR', when used in a reaction involving chlorination
with a mild chlorinating agent, followed by subsequent
halogenation/titanation steps, can result in a more uniform product,
e.g., better catalyst particle size control and distribution.

[0077] Non-limiting examples of species of metal dialkoxides which can be
used include magnesium butoxide, magnesium pentoxide, magnesium hexoxide,
magnesium di(2-ethylhexoxide), and any alkoxide suitable for making the
system soluble.

[0078] As a non-limiting example, magnesium dialkoxide, such as magnesium
di(2-ethylhexoxide), may be produced by reacting an alkyl magnesium
compound (MgRR') with an alcohol (ROH), as shown below.
MgRR'+2R''OH→Mg(OR'')2+RH+R'H

[0079] The reaction can take place at room temperature and the reactants
form a solution. R and R' may each be any alkyl group of 1-10 carbon
atoms, and may be the same or different. Suitable MgRR' compounds
include, for example, diethyl magnesium, dipropyl magnesium, dibutyl
magnesium and butyl ethyl magnesium. The MgRR' compound can be BEM,
wherein RH and RH are butane and ethane, respectively.

[0080] In the practice of the present invention, any alcohol yielding the
desired metal dialkoxide may be utilized. Generally, the alcohol utilized
may be any alcohol of the general formula R''OH where R'' is an alkyl
group of 2-20 carbon atoms, the carbon atoms can be at least 3, at least
4, at least 5, or at least 6 carbon atoms. Non-limiting examples of
suitable alcohols include ethanol, propanol, isopropanol, butanol,
isobutanol, 2-methyl-pentanol, 2-ethylhexanol, etc.

[0081] While it is believed that almost any alcohol may be utilized,
linear or branched, a higher order branched alcohol, for example,
2-ethyl-1-hexanol, can be utilized.

[0082] The amount of alcohol added can vary, such as within a
non-exclusive range of 0 to 10 equivalents, is generally in the range of
about 0.5 equivalents to about 6 equivalents (equivalents are relative to
the magnesium or metal compound throughout), and can be in the range of
about 1 to about 3 equivalents.

[0083] Alkyl metal compounds can result in a high molecular weight species
that is very viscous in solution. This high viscosity may be reduced by
adding to the reaction an aluminum alkyl such as, for example,
triethylaluminum (TEAI), which can disrupt the association between the
individual alkyl metal molecules. The typical ratio of alkyl aluminum to
metal can range from 0.001:1 to 1:1, can be 0.01 to 0.5:1 and also can
range from 0.03:1 to 0.2:1. In addition, an electron donor such as an
ether, for example, diisoamyl ether (DIAE), may be used to further reduce
the viscosity of the alkyl metal. The typical ratio of electron donor to
metal ranges from 0:1 to 10:1 and can range from 0.1:1 to 1:1.

[0084] Agents useful in the step of halogenating the metal alkoxide
include any halogenating agent which when utilized in the present
invention will yield a suitable polyolefin catalyst. The halogenating
step can be a chlorinating step where the halogenating agent contains a
chloride (i.e. is a chlorinating agent).

[0085] Halogenating of the metal alkoxide compound is generally conducted
in a hydrocarbon solvent under an inert atmosphere. Non-limiting examples
of suitable solvents include toluene, heptane, hexane, octane and the
like. In this halogenating step, the mole ratio of metal alkoxide to
halogenating agent is generally in the range of about 6:1 to about 1:3,
can be in the range of about 3:1 to about 1:2, can be in the range of
about 2:1 to about 1:2, and can also be about 1:1.

[0086] The halogenating step is generally carried out at a temperature in
the range of about 0° C. to about 100° C. and for a
reaction time in the range of about 0.5 to about 24 hours.

[0087] The halogenating step can be carried out at a temperature in the
range of about 20° C. to about 90° C. and for a reaction
time in the range of about 1 hour to about 4 hours.

[0088] Once the halogenating step is carried out and the metal alkoxide is
halogenated, the halide product "A" can be subjected to two or more
halogenating/titanating treatments.

[0089] The halogenation/titanation agents utilized can be blends of two
tetra-substituted titanium compounds with all four substituents being the
same and the substituents being a halide or an alkoxide or phenoxide with
2 to 10 carbon atoms, such as TiCl4 or Ti(OR'''')4. The
halogenation/titanation agent utilized can be a chlorination/titanation
agent.

[0090] The halogenation/titanation agent may be a single compound or a
combination of compounds. The method of the present invention provides an
active catalyst after the first halogenation/titanation; however, there
are desirably a total of at least three halogenation/titanation steps.

[0091] The first halogenation/titanation agent is typically a mild
titanation agent, which can be a blend of a titanium halide and an
organic titanate. The first halogenation/titanation agent can be a blend
of TiCl4 and Ti(OBu)4 in a range from 0.5:1 to 6:1
TiCl4/Ti(OBu)4, the ratio can be from 2:1 to 3:1. It is
believed that the blend of titanium halide and organic titanate react to
form a titanium alkoxyhalide, Ti(OR)aXb, where OR and X are
alkoxide and halide, respectively and a+b is the valence of titanium,
which is typically 4.

[0092] In the alternative, the first halogenation/titanation agent may be
a single compound. Examples of a first halogenation/titanation agent are
Ti(OC2H5)3Cl, Ti(OC2H5)2Cl2,
Ti(OC3H7)2Cl2, Ti(OC3H7)3Cl,
Ti(OC4H9)Cl3, Ti(OC6H13)2Cl2,
Ti(OC2H5)2Br2, and Ti(OC12H5)Cl3.

[0093] The first halogenation/titanation step is generally carried out by
first slurrying the halogenation product "A" in a hydrocarbon solvent at
room temperature/ambient temperature. Nonlimiting examples of suitable
hydrocarbons solvent include heptane, hexane, toluene, octane and the
like. The product "A" can be at least partially soluble in the
hydrocarbon solvent.

[0094] A solid product "B" is precipitated at room temperature following
the addition of the halogenation/titanation agent to the soluble product
"A". The amount of halogenation/titanation agent utilized must be
sufficient to precipitate a solid product from the solution. In general,
the amount of halogenation/titanation agent utilized, based on the ratio
of titanium to metal, will generally be in the range of about 0.5 to
about 5, typically in the range of about 1 to about 4, and can be in the
range about 1.5 to about 2.5.

[0095] The solid product "B" precipitated in this first
halogenation/titanation step is then recovered by any suitable recovery
technique, and then washed at room/ambient temperature with a solvent,
such as hexane. Generally, the solid product "B" is washed until the [Ti]
is less than about 100 mmol/L. Within the present invention [Ti]
represents any titanium species capable of acting as a second generation
Ziegler catalyst, which would comprise titanium species that are not part
of the reaction products as described herein. The resulting product "B"
is then subjected to a second and third halogenating/titanating steps to
produce products "C" and "D". After each halogenating/titanating step the
solid product can be washed until the [Ti] is less than a desired amount.
For example, less than about 100 mmol/L, less than about 50 mmol/L, or
less than about 10 mmol/L. After the final halogenating/titanating step,
the product can be washed until the [Ti] is less than a desired amount,
for example, less than about 20 mmol/L, less than about 10 mmol/L, or
less than about 1.0 mmol/L. It is believed that a lower [Ti] can produce
improved catalyst results by reducing the amount of titanium that can act
as a second generation Ziegler species. It is believed that a that a
lower [Ti] can be a factor in producing improved catalyst results such as
a narrower MWD.

[0096] The second halogenation/titanation step is generally carried out by
slurrying the solid product recovered from the first titanation step,
solid product "B", in a hydrocarbon solvent. Hydrocarbon solvents listed
as suitable for the first halogenation/titanation step may be utilized.
The second and third halogenation/titanation steps can utilize a
different compound or combination of compounds from the first
halogenation/titanation step. The second and third
halogenation/titanation steps can utilize the same agent at a
concentration that is stronger than that used in the first
halogenation/titanation agent, but this is not a necessity. The second
and third halogenating/titanating agents can be a titanium halide, such
as titanium tetrachloride (TiCl4). The halogenation/titanation agent
is added to the slurry. The addition can be carried out at ambient/room
temperature, but can also be carried out at temperatures and pressures
other than ambient.

[0097] Generally, the second and third halogenation/titanation agents
comprise titanium tetrachloride. Typically the second and third
halogenation/titanation steps each comprise a titanium to magnesium ratio
in a range of about 0.1 to 5, a ratio of about 2.0 can also be used, and
a ratio of about 1.0 can be used. The third halogenation/titanation step
is generally carried out at room temperature and in a slurry, but can
also be carried out at temperatures and pressures other than ambient.

[0098] The amount of titanium tetrachloride utilized, or alternate
halogenation/titanation agent, may also be expressed in terms of
equivalents, an equivalent herein is amount of titanium relative to the
magnesium or metal compound. The amount of titanium of each of the second
and third halogenating/titanating steps will generally be in the range of
about 0.1 to about 5.0 equivalents, can be in the range of about 0.25 to
about 4 equivalents, typically is in the range of about 0.3 to about 3
equivalents, and it can be desirable to be in the range of about 0.4 to
about 2.0 equivalents. In one particular embodiment, the amount of
titanium tetrachloride utilized in each of the second and third
halogenation/titanation steps is in the range of about 0.45 to about 1.5
equivalent.

[0099] The catalyst component "D" made by the above described process may
be combined with an organometallic catalyst component (a "preactivating
agent") to form a preactivated catalyst system suitable for the
polymerization of olefins. Typically, the preactivating agents which are
used together with the transition metal containing catalyst component "D"
are organometallic compounds such as aluminum alkyls, aluminum alkyl
hydrides, lithium aluminum alkyls, zinc alkyls, magnesium alkyls and the
like. Preferably, the preactivating agent is selected from the group
consisting of trialkylaluminums, dialkylaluminum halides, and
alkylaluminum dihalides.

[0100] The preactivating agent is preferably an organoaluminum compound.
The organoaluminum preactivating agent is typically an aluminum alkyl of
the formula AlR3 wherein at least one R is an alkyl having 1-8
carbon atoms or a halide, and wherein each of the R may be the same or
different. Suitable preactivating agents include trialkyl aluminum such
as, for example, trimethyl aluminum (TMA), triethylaluminum (TEAL),
triisobutylaluminum (TIBAL) and also include diethylaluminum chloride,
triisobutylaluminum chloride, butylaluminum dichloride, and the like, and
mixtures thereof. The organoaluminum preactivating agent is more
preferably trimethyl aluminum (TMA), triethyl aluminum (TEAL),
triisobutyl aluminum (TIBAL) or mixtures thereof. Preferably, the
preactivating agent is TEAL, since with TEAL the molecular weight
distribution (MWD) of the bimodal polyethylene prepared in the two
reactors in series is even wider than when using other organoaluminum
preactivating agents. Generally, when using TEAL as the preactivating
agent the MWD will be at least 4.

[0101] In general, the ratio of Al to titanium can be in the range from
0.1:1 to 2:1 and typically is O. 25:1 to 1.2:1.

[0102] Optionally, the Ziegler-Natta catalyst may be pre-polymerized.
Generally, a prepolymerization process is affected by contacting a small
amount of monomer with the catalyst after the catalyst has been contacted
with the preactivating agent. A pre-polymerization process is described
in U.S. Pat. Nos. 5,106,804; 5,153,158; and 5,594,071, hereby
incorporated by reference.

[0103] Optionally, an electron donor may be added with the halogenation
agent, the first halogenation/titanation agent, or the subsequent
halogenation/titanation agent or agents. It may be desirable to have an
electron donor utilized in the second halogenation/titanation step.
Electron donors for use in the preparation of polyolefin catalysts are
well known, and any suitable electron donor may be utilized in the
present invention that will provide a suitable catalyst. Electron donors,
also known as Lewis bases, are organic compounds of oxygen, nitrogen,
phosphorous, or sulfur which can donate an electron pair to the catalyst.

[0104] The electron donor may be a monofunctional or polyfunctional
compound, can be selected from among the aliphatic or aromatic carboxylic
acids and their alkyl esters, the aliphatic or cyclic ethers, ketones,
vinyl esters, acryl derivatives, particularly alkyl acrylates or
methacrylates and silanes. An example of a suitable electron donor is
di-n-butyl phthalate. A generic example of a suitable electron donor is
an alkylsilylalkoxide of the general formula RSi(OR')3, e.g.,
methylsilyltriethoxide [MeSi(OEt3)], where R and R' are alkyls with
1-5 carbon atoms and may be the same or different.

[0105] For the polymerization process, an internal electron donor can be
used in the synthesis of the catalyst and an external electron donor or
stereoselectivity control agent (SCA) to activate the catalyst at
polymerization. An internal electron donor may be used in the formation
reaction of the catalyst during the halogenation or
halogenation/titanation steps. Compounds suitable as internal electron
donors for preparing conventional supported Ziegler-Natta catalyst
components include ethers, diethers, ketones, lactones, electron donors
compounds with N, P and/or S atoms and specific classes of esters.
Particularly suitable are the esters of phthalic acid, such as
diisobutyl, dioctyl, diphenyl and benzylbutylphthalate; esters of malonic
acid, such as diisobutyl and diethylmalonate; alkyl and arylpivalates;
alkyl, cycloalkyl and arylmaleates; alkyl and aryl carbonates such as
diisobutyl, ethyl-phenyl and diphenylcarbonate; succinic acid esters,
such as mono and diethyl succinate.

[0106] External donors which may be utilized in the preparation of a
catalyst according to the present invention include organosilane
compounds such as alkoxysilanes of general formula
SiRm(OR')4-m, where R is selected from the group consisting of
an alkyl group, a cycloalkyl group, an aryl group and a vinyl group; R'
is an alkyl group; and m is 0-3, wherein R may be identical with R'; when
m is 0, 1 or 2, the R' groups may be identical or different; and when m
is 2 or 3, the R groups may be identical or different.

[0107] The external donor of the present invention can be selected from a
silane compound of the following formula: wherein R1 and R4 are
both an alkyl or cycloalkyl group containing a primary, secondary or
tertiary carbon atom attached to the silicon, R1 and R4 being
the same or different; R2 and R3 are alkyl or aryl groups.
R1 may be methyl, isopropyl, cyclopentyl, cyclohexyl or t-butyl;
R2 and R3 may be methyl, ethyl, propyl, or butyl groups and not
necessarily the same; and R4 may also methyl, isopropyl,
cyclopentyl, cyclohexyl or t-butyl. Specific external donors are
cyclohexylmethyldimethoxy silane (CMDS), diisopropyldimethoxysilane
(DIDS) cyclohexylisopropyl dimethoxysilane (CIDS),
dicyclopentyldimethoxysilane (CPDS) or di-t-butyl dimethoxysilane (DTDS).

[0108] According to the present invention the polyethylene resin is
prepared in two or more serially connected reactors, preferably loop
reactors, more preferably slurry loop reactors, most preferably liquid
full loop reactors in the presence of same or different Ziegler-Natta
catalyst systems.

[0109] Preferably, the high density and low density fractions are produced
in two serially connected loop reactors with the same catalyst system.
While preferably the HMW polyethylene fraction is produced in the first
reactor and the LMW polyethylene fraction is produced in the second
reactor, the opposite order is also possible. That is, the lower
molecular weight polyethylene can also be produced in the first of the
two reactors connected in series. The Mw in each of the zones can be
regulated by known techniques such as choice of catalyst, reactor
temperature, and amount of hydrogen used.

[0110] The catalyst system may be employed in a solution polymerisation
process, a slurry polymerisation process or a gas phase polymerisation
process. Preferably a slurry process is used. The most preferred
polymerisation process is carried out in two serially connected slurry
loop reactors, advantageously liquid full loop reactors i.e. a double
loop reactor.

[0111] In a preferred arrangement, the product of a first reactor,
including the olefin monomer, is contacted with the second co-reactant
and the catalyst system in a second reactor to produce and mix the second
polyolefin with the first polyolefin in the second reactor. This is also
known as a chemical blend. The first and second reactors are conveniently
interconnected, i.e. serially connected, reactors such as interconnected
loop reactors. It is also possible to introduce into the second reactor
fresh olefin monomer as well as the product of the first reactor.

[0112] Because the second polyolefin is produced in the presence of the
first polyolefin a multimodal or at least bimodal molecular weight
distribution is obtained.

[0113] In one embodiment of the invention, the first co-reactant in the
first reactor is hydrogen, to produce the LMW fraction and the second
co-reactant in the second reactor is the comonomer to produce the HMW
fraction. Typical comonomers include hexene, butene, octene or
methylpentene, preferably hexene.

[0114] In an alternative embodiment, the first co-reactant in the first
reactor is the comonomer, preferably hexene. Homopolymerisation then
takes place in the second reactor with little or no interference from the
comonomer. Preferably, unreacted comonomer is removed before the
polyethylene fraction from the first reactor is transferred to the second
reactor.

[0115] The temperature in each reactor may be in the range of from
60° C. to 110° C., preferably from 78° C. to
98° C.

[0116] The high molecular weight, low density fraction has a density of at
least 0.908 g/cm3, preferably of at least 0.922 g/cm3 and of at
most 0.938 g/cm3, more preferably of at most 0.945 g/cm3. Most
preferably it is of about 0.936 g/ cm3. It has a high load melt
index HL275 of at least 1.5 dg/min, more preferably of at least 5 dg/min
and most preferably of at least 7 dg/min and of at most 14 dg/min, more
preferably of at most 10 dg/min. Most preferably, it is of 8 to 9 dg/min.
The HLMI can be calculated from the HL275 by:

HLMI=HL275/3.2

[0117] The low molecular weight, high density fraction has a density of at
least 0.953 g/cm3, more preferably of at least 0.957 g/cm3, and
of at most 0.978 g/cm3, more preferably of at most 0.962 g/cm3.
Most preferably it is of about 0.957 to 0.976 g/ cm3.

[0118] The HLMI and density of the fraction in the second reactor were
determined using the following formula:

wherein [0119] "final" means "of the polyethylene resin" [0120] "1st"
means "of the polyethylene fraction produced in the first reactor" [0121]
"2nd" means "of the polyethylene fraction produced in the second reactor,
downstream of the first reactor"

[0122] The final resin according to the invention has a density of from
0.950 to 0.965 g/cm3, preferably 0.952 to 0.962 g/cm3, more
preferably 0.954 to 0.962 g/cm3 and most preferably 0.957 to 0.960
g/cm3. The polyethylene resin has a melt index MI2 of from 0.5 to 5
g/10 min, preferably 0.8 to 3 g/10 min.

[0123] Density is measured according to ASTM 1505 at a temperature of
23° C.

[0124] HL275 is measured according to ASTM D 1238 at a temperature of
190° C. and under a load of 21.6 kg, except that a die of 2.75 mm
broad instead of 2.1 mm was used.

HLMI=HL275/3.2

[0125] The melt index MI2 and high load melt index HLMI are measured by
the method of standard test ASTM D 1238 respectively under a load of 2.16
kg and 21.6 kg and at a temperature of 190° C.

[0126] The molecular weight distribution is defined by the ratio Mw/Mn of
the weight average molecular weight Mw to the number average molecular
weight Mn as determined by gel permeation chromatography (GPC).

[0127] Preferably the polyethylene resin comprises 36 to 50 wt % of HMW
fraction, preferably from 38 to 46 wt %, more preferably from 40 to 43 wt
% and from 50 to 64 wt % of LMW fraction, preferably from 54 to 62 wt %
and most preferably from 57 to 60 wt %. The molecular weight distribution
is preferably of from 5 to 20, more preferably of from 8 to 16, most
preferably of from 10 to 14. The most preferred polyethylene resin
according to the present invention has a density of about 0.959
g/cm3 and a melt index MI2 of about 0.8-1.8 g/10 min and a molecular
weight distribution of about 10-14.

[0128] The polyethylene resin may contain additives such as, by way of
example, antioxidants, light stabilizers, acid scavengers, lubricants,
antistatic additives, nucleating/clarifying agents, and colorants. An
overview of such additives may be found in Plastics Additives Handbook,
ed. H. Zweifel, 5th edition, 2001, Hanser Publishers.

[0129] Injection-Stretch Blow Molding

[0130] The polyethylene resin according to the invention is particularly
suitable for injection stretch blow molding applications. In particular,
it provides a broad processing window, good process stability to prepare
containers with good thickness repartition, good surface aspects, good
finishing, high ESCR and a high top load.

[0131] The injection-stretch blow molding process of the present invention
can either be a one-stage or a two-stage process. in a one-stage process
injection molding of the preform and blowing of the preform to the final
desired shape are performed on the same machine, whereas in a two-stage
process injection-molding of the preform and blowing of the preform are
conducted in different machines, which can be separated by a long
distance. Thus, the two-stage process additionally requires the cooling
of the preform to ambient temperature and a subsequent reheating before
the blowing step.

[0132] It has now been surprisingly found that under stretching and
blowing conditions similar to those used for polyethylene terephthalate,
containers with high rigidity, high ESCR and high impact resistance can
be obtained.

[0133] The polyethylene resins according to the invention, having such a
specific composition, molecular weight and density, can lead to a marked
improvement of the processing properties when the resin is used in
injection-stretched-blow-moulding, while conserving or improving
mechanical behaviour as compared to the same articles prepared with other
resins.

[0134] The present invention also comprises the method for preparing
preforms, the preforms so obtained, the use of said preforms for
preparing containers, and the containers prepared from said preforms.

[0135] Polyethylene resin is generally not used in
injection-stretch-blow-moulding applications and the
injection-stretch-blow-moulding conditions are thus adapted accordingly.

[0136] The preform, which has an open and a closed end, is prepared by
injection molding. For the present invention the polyethylene resin
according to the invention is fed to an extruder, plasticized and
injected under pressure into an injection mold through an opening,
generally referred to as "gate". The polyethylene resin is injected into
the injection mold at an injection temperature of at least 220°
C., preferably of at least 230° C. The injection temperature is at
most 300° C., preferably at most 290° C. and most
preferably at most 280° C. The choice of injection temperature
depends upon the melt flow index of the polyethylene resin. It is clear
to the skilled person that a lower melt flow index requires a higher
injection temperature and vice versa. The injection mold is filled at
such a rate as to give a ratio of mold filing rate (in cm3/s) over
gate size (in mm) of 15 or less, preferably of 10 or less. The preform is
cooled inside the injection mold and removed from it. The ratio of mold
filling rate over gate size varies depending upon the viscosity of the
molten polyethylene resin, i.e. a more viscous molten polyethylene resin
requires a lower value for the ratio than a more fluid molten
polyethylene resin, so that a preform with good processing properties in
the subsequent stretch-blowing steps will be obtained.

[0137] The two-step process comprises the steps of: [0138] providing a
preform by injection moulding on a mould, preferably on a multi-cavity
mould; [0139] cooling the preform to room temperature; [0140]
transporting the preform to the blow moulding machine; [0141] reheating
the preform in the blow moulding machine in a reflective radiant heat
oven [0142] optionally, passing the heated preform through an
equilibration zone to allow the heat to disperse evenly through the
preform wall; [0143] optionally, submitting the preform to a pre-blow
step; [0144] stretching the preform axially by a centre rod; [0145]
orienting the stretched preform radially by high pressure air.

[0146] The one-step process comprises the steps of: [0147] providing a
pre-form by injection moulding on a mould, preferably on a multi-cavity
mould; [0148] optionally slightly re-heating the pre-form; [0149]
optionally, passing the heated pre-form through an equilibration zone to
allow the heat to disperse evenly through the pre-form wall; [0150]
optionally, submitting the preform to a pre-blow step; [0151] stretching
the pre-form axially by a centre rod; [0152] orienting the stretched
pre-form radially by high pressure air.

[0153] In a one-stage process the preform is cooled to a temperature in
the range from 90° C. to 140° C. and is stretch-blown into
a container. All of these steps are performed on a single machine.

[0154] In a two-stage process the preform is allowed to cool to ambient
temperature and transported to a different machine. The preforms are
uniformly reheated to a temperature below the polyethylene's melting
point. The reheating can be followed by an equilibration step.
Subsequently, the preform is transferred to the stretch-blowing zone and
secured within the blowing mold, which has the same shape as the final
container, in such a way that the closed end of the preform points to the
inside of the blowing mold. The preform is stretched axially with a
center rod, generally referred to as "stretch rod" to bring the wall of
the perform against the inside wall of the blowing mold. The stretch rod
speed can go up to 2000 mm/s. Preferably it is in the range from 100 mm/s
to 2000 mm/s, and more preferably in the range from 500 mm/s to 1500
mm/s. Pressurized gas is used to radially blow the preform into the
blowing mold shape. The blowing is done using gas with a pressure in the
range from 5 bars to 40 bars, and preferably from 10 bars to 30 bars.

[0155] The blowing of the preform can also be performed in two steps, by
first pre-blowing the preform with a lower gas pressure, and then blowing
the preform to its final shape with a higher gas pressure. The gas
pressure in the pre-blowing step is in the range from 2 bars to 10 bars,
preferably in the range from 4 bars to 6 bars. The preform is blown into
its final shape using gas with a pressure in the range from 5 bars to 40
bars, more preferably from 10 bars to 30 bars, and most preferably from
15 bars to 25 bars.

[0156] Following the stretching and blowing, the container is rapidly
cooled and removed from the blowing mold.

[0157] The containers obtained by the injection-stretch blow molding
process of the present invention are characterized by good impact
properties in combination with high rigidity and high ESCR.

[0158] The articles prepared according to the present invention are hollow
containers and bottles that can be used in various food and non-food
applications, in particular for consumer packaging. The food applications
comprise in particular the storage of juices, dry products and dairy
products. The non-food applications comprise in particular the storage of
cosmetic, detergents and pharmaceutical products.

EXAMPLES

Example 1

[0159] 1. Pellet Properties

[0160] The polyethylene resins of Grades X and Y have a bimodal molecular
weight distribution produced in two serially connected slurry loop
reactors i.e. a double loop reactor using a Ziegler-Natta catalyst system
and thus comprises two polyethylene fractions. The GPC are shown in FIG.
1. Grade Z is a polyethylene resin produced in the presence of a
metallocene catalyst. Grades X and Z are comparative examples.

[0162] The density was measured according to the method of standard test
ASTM 1505 at a temperature of 23° C. The melt index M12 and high
load melt index HLMI were measured by the method of standard test ASTM D
1238 respectively under a load of 2.16 kg and 21.6 kg and at a
temperature of 190° C.

[0163] ESCR was measured according to ASTM D 1693 using 100% Igepal CO-630
as a chemical agent.

[0165] The swell is measured on a Gottfert 2002 capillary rheometer
according to ISO11443:2005 with the proviso that the extruded samples
were 10 cm long instead of 5 cm long. The method involves measuring the
diameter of the extruded product at different shear velocities. The
capillary selection corresponds to a die having an effective length of 10
mm, a diameter of 2 mm and an aperture of 180°. The temperature is
210° C. Shear velocities range from 7 to 715 s -1, selected
in decreasing order in order to reduce the time spent in the cylinder; 7
velocities are usually tested. When the extruded product has a length of
about 10 cm, it is cut, after the pressure has been stabilised and the
next velocity is selected. The extruded product (sample) is allowed to
cool down in a rectilinear position.

[0166] The diameter of the extruded product is then measured with an
accuracy of 0.01 mm using a vernier, at 2.5 cm (d2.5) and at 5 cm
(d5) from one end of the sample, making at each position d2.5
and d5 two measurements separated by an angle of 90°,

[0167] The diameter do the one end of the sample selected for the
test is extrapolated:

do=d2.5+(d2.5-d5)

[0168] The swell G is determined as

G=100×(do-df)/df

wherein df is the die diameter.

[0169] The swell value is measured for each of the selected shear
velocities and a graph representing the swell as a function of shear
velocity can be obtained.

[0170] With Grade Z which also has a higher melt flow, it was impossible
to obtain an acceptable injection stretch blow moulded container, see
FIG. 2.

[0171] 2. Injection Process

[0172] A preform (22 g) was injected with each of Grades X and Y as
described in Example 1, Table 1, and a standard commercial polyethylene
terephthalate (PET) on Arburg mono cavity machine.

[0177] After this, these preforms were transformed into bottles by
stretching and blowing.

[0178] 3. Stretching/Blowing Process

[0179] Bottles of 1 Litre were blown on a SIDEL SBO8 series 2. All tests
were realized with industrial equipments and industrial conditions (1700
b/h). The heating was realized using a standard heating process as
conventionally used for PET. The pressure during blowing was at 15 bar.

[0180] From the preform and bottle designs, the length ratio (3.09) and
hoop ratio (2.75) can be calculated.

[0182] The drop tests were carried out with bottles filled with 1 litre of
water at room temperature. The bottles were then dropped from increasing
height, until 50% of the bottles dropped were cracked.

[0188] We show here that Grade Y according to the invention has properties
comparable to PET. Moreover the moulded drawings (engravings) are much
more accurate with Grade Y according to the invention than when using
PET.

Example 2

[0189] Furthermore, FIGS. 6 and 7 show bottle schematics and a full view
of an ISBM bottle prepared with the resin according to the invention i.e.
Grade Y . It was observed that even mouldings with dimensional
restrictions i.e. narrower portions, can be successfully made using the
resin of the invention. Furthermore, it was observed that bottles of 100
dm3 with a weight of only 22 g could be obtained, whilst maintaining
all other properties. Thus the resin according to the invention enables
overall reduction in weight without deteriorating other properties of an
ISBM bottle.